
I may have struck out with Arlecchino but I'm not going to let that stop me. Although I guess it's easier to make predictions on stuff with not too much information whose release is far far away lol
Anyway I noticed that a few of the Fatui are actually modeled after the same fundamental character. Previously I said that the Capitano character ends up being part of 3 of the Harbingers: Scaramouche, Signora and Capitano himself. Scara is an evolution on the character while Signora was just given some of the characteristics to flesh out her otherwise simple personality. Pulcinella is also in this box. He's one of the Zanni stock characters along with Brighella, Arlecchino and Pierro himself.
We already know that Pierro is the fool but Genshin's likely portraying that as deliberate. Arlecchino is actually a fool while Brighella might be playing a role in between the two.
Pulcinella is a little different. Outwardly he's just like Arlecchino but that's because he's got other motives. We can actually see that from how he's the one that brought Childe into the Harbingers and he did it while telling him it was a punishment. Childe has so far become a valuable asset to the Fatui. My guess is Pulcinella will constantly feign ignorance so you can't prove he did anything even when the outcomes make it feel very obvious.
This should go very well with his appearance in Fontaine since we have to deal with the God of Justice who likes flaunting her courtroom. Could it be that we'll not only have to defend ourselves against the unjust accusations of her system but maybe also Pulcinella who figures out how to work the system?
There is also a common theme of the Heavenly Principles. We saw in Inazuma how Ei's faith in them is what led her to believing in Eternity and that's why she ends up passing the Sakoku and Vision Hunt Decrees. This ended up also a manipulation by the Fatui who were praying on her fear of loss. In Sumeru I theorize that it'll be Kusanali who wants to figure out the Heavenly Principles and Celestia's motive for enacting them. Because of this she'll allow the Fatui to continue their operations. The Hydro Archon is in the same boat as Ei not wanting to go against the principles. While it seems she at least knows they're wrong she doesn't dare to go against them and I guessed she'll probably falsely accuse anybody who she thinks could get her on the bad side of Celestia.
The story could play out that Pulcinella plays with that for his own ends incriminating people that either find out about the Fatui operations or are targets he can't eliminate privately. With help from Lyney and Lynette and a Fontaine resistance we'll eventually convince the Archon but thanks to Pulcinella even she can't figure out how to arrive at an innocent verdict.
It'd be really funny if it does actually play out like a courtroom. We take to the stand with Lyney and Lynette as our legal counsel while Pulcinella is the prosecutor. As the battle goes on we kinda Danganronpa and prove Pulcinella's guilt which causes him to flee and then we have to bring him to justice weekly boss style.

Tips and Tricks from a Super Casual Genshin f2p

